S55 crankhub and timing guide
Factory torque specs, grip-disc law, special tools, and honest job sequences for the S55 crankhub, damper, timing chain, and VANOS adjusters — from ISTA.
The S55 is the N55 architecture turned up, and BMW M's version of the crankhub comes with the strictest replace-not-reuse list in the six-cylinder data. The factory docs name a >600 Nm breakaway torque on the central bolt, a hardened friction stack they call grip discs, and a hub-replacement procedure that starts with "remove engine." Here is what ISTA actually specifies, traced to document ids.
The grip-disc law
This is the headline of the S55 chain and hub procedures, in the factory's own structure. After each release of the central bolt on the crankshaft, the following must be renewed without fail:
- The central bolt
- The Eka grip disc
- The camshaft sprocket with the welded-on Eka grip discs
- The camshaft sprocket for the timing chain drive
The hub procedure repeats it: absolutely necessary to renew all grip discs after releasing the central bolt. The friction path between hub, sprockets, and crank is the design — and the document treats the stack as consumable the moment it is unloaded.
Crankhub torque table
| Fastener | Thread | Spec | Torque |
|---|---|---|---|
| Hub (torsion damper) to crankshaft, central bolt 12.9 | M18 x 108 | Replace. Lightly oil screw and thread | 100 Nm (73.8 lb-ft) + 270° |
| Vibration damper to crankshaft hub, screws 10.9 | M8 x 20 | Replace screw | 20 Nm (14.8 lb-ft) + 90° |
Note the damper screws differ from the N55's: longer (M8 x 20 vs M8 x 16), torque-plus-angle instead of straight torque, and replace-not-reuse. Tighten them in the factory sequence, 1 to 8.
Damper off vs hub off
- **Damper R&R (`11 23 010`):** belt off, screws out, damper off — then the factory adds a step most guides skip: *visually check the hub for damage and renew as needed.* Damper screws back in sequence 1–8 at 20 Nm + 90°.
- **Hub replacement (`11 31 051` hub variant):** engine out and on the assembly stand. Cylinder head cover, spark plugs, belt tensioner, damper, front crank seal, timing check, oil-pump chain tensioner sealing cap, vacuum pump sealing cover, and the oil sump all come off first. The oil pump's central bolt is released with the sprocket blocked by tool `2 303 793`, after the hydraulic chain tensioner is drained (press the tensioning rail repeatedly — pulsating drain — then lock the piston with a 2.5–3 mm pin). Then the hub moves forward off the crank.
Timing chain, guides, and tensioner
| Fastener | Thread | Torque |
|---|---|---|
| Chain drive module to cylinder head | M6 x 35 | 8 Nm (5.9 lb-ft) |
| Guide rail to crankcase | M8 | 20 Nm (14.8 lb-ft) |
| Guide rail to cylinder head | M7 | 14 Nm (10.3 lb-ft) |
| Chain tensioner to cylinder head | M22 x 1.5 | 55 Nm (40.6 lb-ft) |
| Screw plug in cylinder head | M18 x 1.5 | 25 Nm (18.4 lb-ft) |
| Eccentric shaft bearing cap to cylinder head | M6 x 27 | 8.6 Nm (6.3 lb-ft) |
| Camshaft bearing cap (intake head) | M6 x 30.5 | 8.6 Nm (6.3 lb-ft) |
| Exhaust camshaft bearing strips (steel screw 10.9) | M7 x 70 | 8 Nm (5.9 lb-ft) + 60°, inserted dry |
| Sprocket to oil pump | M8 | 20 Nm (14.8 lb-ft) + 45° |
| Oil pump to bedplate | M8 x 123 | Replace; thread repairs only with Al Helicoil; 10 Nm (7.4 lb-ft) + 180° |
VANOS adjusters
| Fastener | Thread | Spec | Torque |
|---|---|---|---|
| VANOS with sensor gear to inlet and exhaust camshafts | M10 x 94 | Replace screw | 20 Nm (14.8 lb-ft) + 180° |
Setting the timing after the hub job: replace both camshaft central bolts, rotate the camshaft sensor wheel until the retaining pins line up with tool 11 4 290, slide the fixture on and bolt it down, screw both central bolts in and release them 90°, pre-tension the chain with 11 9 340 at 0.6 Nm (0.4 lb-ft) (00 9 250), then torque the adjuster bolts with 00 9 120. Crank twice, re-check.
Special tools
- `11 0 300` — TDC locking (removed to release the central bolt, per the doc)
- `11 4 280` — remounted "for the S55 engine" as the counterhold, with `11 4 281` camshaft locks
- `11 9 260` / `11 8 180` / `11 8 660` — crank blocking (engine out / manual / automatic)
- `11 8 650` — bolts to the belt-tensioner mount; used with `11 0 290` to hold the camshaft sprocket
- `11 0 290` — camshaft sprocket lock
- `2 303 793` — oil pump sprocket block (crankcase-mounted)
- `11 8 640` — releases the aluminium screw on the chain module
- `11 4 290` — sensor-wheel alignment fixture for timing set
- `11 9 340` + `00 9 250` + `00 9 120` — pre-tension and bolt-torque set
- `11 4 480` / `11 4 481` / `11 4 284` / `11 4 285` — adjuster-job fixtures (`11 36 046`)
Coverage notes
Straight answer on coverage: the S55 is well served in the data — damper, hub, chain, tensioner, adjusters, and timing check procedures all exist with full torque tables, plus the S55-specific grip-disc renewal law and the >600 Nm breakaway spec. What the data does not carry is a wear limit for grip discs, a service interval, or failure-mileage statistics — the renewal law is conditional on opening the bolt, not on a mileage clock. Nothing here supports inventing one.
Every number traces to the ISTA ids in the sources. The full procedures — especially the engine-out hub job — live in ISTA; this page is the numbers sheet and the parts-to-order list.
- 11 23 010 — Removing and installing/replacing vibration damper (S55)
- 11 31 051 — Replace the hub for the vibration damper (S55)
- 11 31 051 — Replacing timing chain (S55)
- 11 31 090 — Installing and removing/replacing chain tensioner piston (S55)
- 11 31 005 — Checking camshaft timing (S55)
- 11 36 046 — Removing and installing or replacing intake and exhaust camshaft adjusters (S55)
- 11 21 1AZ — Torsion damper (hub) to crankshaft, central bolt (S55)
- 11 23 1AZ — Vibration damper to crankshaft hub screws (S55)
- 11 31 2–8AZ — Chain drive module, rails, chain tensioner, caps (S55)
- 11 36 1AZ — VANOS with sensor gear to inlet and exhaust camshafts (S55)
- 11 41 9AZ — Sprocket to oil pump (S55)